Alloys of antimony and selenium used in photoconductive elements



M. B. MYERS ET AL ALLOYS OF ANTIMONY AND SELENIUM USED IN PHOTOOONDUCTIVE ELEMENTS Filed July 20, 1966 Jan. 20, 1970 8g 8 &3 8% am 6 m am 8 6 am mm m am am 5 8 3 Pm am 6 3 am 3 w t 2 Q9 N t m. on 2 09 .N t n. Qm 2 8. .N t m. on B 09 E E f. I C E r. E I Z I C o o 3 ts 202.6228 L L 0 3 Q3 o 0 9 0 9 o ow om QM o /O ow -N n v. 96 E w zQ Qmmqm 1 wwzomwwm M25 51 -m IQ L l L. on w 55E C Ewzwm o. L. IAN.

INVENTORS B. MYERS JAMES W. SPARKS EVAN J United States Patent 3,490,903 ALLOYS 0F ANTIMONY AND SELENIUM USED IN PHOTOCONDUCTIVE ELEMENTS Mark B. Myers, Penfield, and James W. Sparks and Evan J. Felty, Rochester, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed July 20, 1966, Ser. No. 566,593 Int. Cl. G03g 5/04 U.S. Cl. 961.5 12 Claims ABSTRACT OF THE DISCLOSURE A photoconductive insulating layer comprising a vitreous alloy of antimony and selenium, with the antimony being present in a concentration of from about 5 to 25 percent and the method of imaging a xerographic plate containing the antimony-selenium composition.

This invention relates in general to the art of xerography, and in particular, to a new photosensitive element.

In the art of xerography it is usual to form an electrostatic latent image on a member or plate which comprises a conductive backing such as, for example, a metallic surface having a photoconductive insulating layer thereon. A suitable plate for this purpose is a metallic member having thereon a layer of vitreous selenium. Such a plate is characterized by being capable of receiving a satisfactory electrostatic charge and selectively dissipating such a charge when exposed to a light pattern and, in general, is largely sensitive to light in the bluegreen spectral range.

Although vitreous selenium for the most part has become the standard in commercial xerography, many of its properties can be improved by the addition of alloying; elements which enhance such properties as spectral response, light sensitivity, photoconductive stability, etc., U.S. Patents 2,803,542 to Ullrich, and 2,822,300 to Mayer et al. both show the advantages of modifying vitreous selenium by the addition of appreciable amounts of arsenic in order to yield a broader range of spectral sensitivity increase the overall photographic speed, and in general improve the stability of the photoconductive layer.

Although vitreous selenium shows a satisfactory sensitivity, the need for photoconductors exhibiting increased sensitivity and spectral response exceeding those of vitreous selenium is needed in high speed processes which require plates having a very high degree of sensitivity due to the short time factor in rapid cycling.

It is, therefore, the object of this invention to provide an improved system for utilizing a novel photoconductor which overcomes the above noted disadvantages.

It is a further object of this invention to provide a system utilizing a photoconductor having improved xerographic properties.

It is another object of this invention to provide an improved photoconductor having a high spectral response.

It is a further object of this invention to provide a xerographic plate having a high sensitivity factor.

It is another object of this invention to provide an improved photosensitive element.

It is yet another object of this invention to provide a novel composition having enhanced photoconductive properties.

The foregoing objects and others are accomplished in accordance with this invention by providing a novel vitreous antimony selenium alloy for use as a photoconductor. These alloys are prepared in a manner similar to those vitreous photoconductive alloys of the arsenic-selenium system such as those described in U.S. Patents 2,803,542 and 2,822,300, already mentioned above.

3,490,903 Patented Jan. 20, 1970 It has been discovered that a vitreous alloy of antimony and selenium in an effective range of about 5 to 21 percent by weight antimony, with the remainder substantially selenium, yields a photosensitive composition having a sensitivity factor (to be more fully described later) up to 12 times greater than that of vitreous selenium, and in addition having a relative response up to three times that of vitreous selenium in the blue-green spectral range. A preferred range of about 7 to 19 percent antimony yields the greatest sensitivity factor while, at about 14 percent antimony the maximum sensitivity of a factor of 12 is reached. Percentages of antimony less than about 5 percent and more than about 21 percent yield no increase in sensitivity or spectral response over that of substantially pure vitreous selenium.

The advantages of the improved photosensitive composition will become apparent upon consideration of the following disclosure of the invention; especially when taken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a graphical illustration of the sensitivity factor of vitreous selenium as compared with various percentages of antimony, and selenium as contemplated by this invention.

FIGURE 2 is a graphical illustration of the relative response of the antimony-selenium alloys contemplated by this invention as compared with vitreous selenium.

The antimony-selenium vitreous alloys of this invention may be prepared by any suitable techniques. Typical techniques are co-evaporation, wherein the appropriate amount of selenium and antimony are each separately placed in heated crucibles maintained in a vacuum chamber under any suitable vacuum conditions such as from about 2X10- to 2x10 millimeters of mercury.

The crucibles may be made of any inert material such as quartz or ceramic lined metal. The selenium and antimony are each maintained at a temperature between about their respective melting points and boiling points. Thus, for example, in forming a vitreous antimony-selenium alloy containing about 14 percent antimony and 86 percent selenium, a temperature of about 290 C. for selenium, and 660 C. for antimony, was found sufiicient. To increase the amount of antimony in the alloy, the temperature of the antimony containing crucible would be increased and/ or the temperature of the selenium containing crucible lowered. To increase the amount of selenium in the alloy the temperature changes would be reversed.

If a very slow rate of evaporation is desired, the evaporation temperature of one or both of the components may be maintained at a temperature below their melting point.

Under the above conditions, a film thickness of about 10 to 40 microns is obtained when evaporation is continued for a time ranging from about 1 to 3 hours at a vacuum of about 5 X 10- mm. of mercury.

A substrate is supported above the heated crucibles upon which the antimony and the selenium are co-evaporated. A suitable substrate temperature is from about 50 to C.

Another typical method includes flash evaporation under vacuum conditions similar to those defined in coevaporation, wherein an alloy of selenium and antimony having a particle size of about less than about 0.1 mm. in diameter is selectively dropped into a heated inert crucible maintained at a temperature of about 450 to 550 C. The vapors formed by the heated mixture are evaporated upward onto a substrate supported above the crucible. The substrate is maintained at a temperature of about 50 to 70 C. This procedure is continued until 3 the desired thickness of the vitreous antimony-selenium alloy has been formed on the substrate.

The alloys of this invention may be conveniently formed on any conductive substrate. This may be a conventional metal plate such as brass, aluminum, gold, platinum, steel or the like. The support member may be of any convenient thickness, rigid or flexible, in the form of a sheet, a web, a cylinder, or the like and may be coated with a thin layer of plastic. It may also comprise such materials as metallized paper, plastic sheets covered with a thin coating of aluminum or copper iodide, or glass coated with a thin layer of chromium or tin oxide. In certain cases, the substrate may even be dispensed with, if desired.

The thickness of the antimony-selenium vitreous alloy layer for use as a photoconductor is not critical. The layer can be as thin as a micron, or as great as 300 microns or more, but for most applications the thickness will generally be about 20 to 80 microns.

The following examples further specifically define the present invention with respect to the method of making an antimony-selenium photosensitive element. The percentages in the disclosure, examples, and claims are by weight unless otherwise indicated. The examples below are intended to illustrate various preferred embodiments of making an antimony-selenium photoconductor.

EXAMPLE I An alloy of about 20 percent antimony and 80 percent selenium is ground in a ball mill and then placed in a brass hopper containing a copper chute adapted to deliver particles, up to 0.1 cm. in diameter, into a quartz crucible maintained below said hopper. The quartz crucible is surrounded with a resistance heater controlled to heat the crucible to a temperature of about 490 C. An aluminum substrate placed on a base and maintained at a temperature about 55 C. is positioned about 12 inches above the quartz crucible. A bell jar is then placed over the hopper, crucible, and substrate, and evacuated to a vacuum of about 5 10 millimeters of mercury, and the quartz crucible heated to a temperature of 490 C. When the quartz crucible is brought to 490 C. the hopper door below the chute leading to the quartz crucible is opened allowing a small sample of the antimony-selenium mixture to pour into the quartz crucible. The antimonyselenium mixture rapidly evaporates causing vapors of antimony and selenium to come into contact with the suspended aluminum substrate. This process is continued for about 2 hours at which time a 15 micron layer of antimony-selenium containing about 20 percent antimony has been formed on the aluminum substrate. The crucible is then allowed to cool to room temperature, the vacuum broken, and the coated substrate removed from the vacuum chamber.

EXAMPLE II A 40 micron film of vitreous antimony-selenium on a NESA substrate containing about 10 percent antimony and 90 percent selenium is prepared by placing 20 gm. samples of antimony and selenium in the form of pellets into separate quartz crucibles. The quartz crucibles are placed into a vacuum chamber which is evacuated to'a vacuum of about 5X10 millimeters of mercury. A substrate of NESA glass is suspended about 12 inches above the quartz crucibles and maintained at a temperature of about 55 C. The antimony and selenium are co-evaporated onto the NESA substrate by maintaining the temperature of the selenium crucible at about 290 C. and the temperature of the antimony crucible at about 602 C. by means of resistance heating elements. The quartz crucibles containing the antimony and selenium samples are maintained at these temperatures for about 1 hours at which time the evaporation is complete. The crucibles.

are cooled to room temperature, the vacuum is then broken, and the antimony-selenium coated NESA plate removed from the vacuum chamber.

4 EXAMPLE In The vitreous-selenium coated plate formed by the method of Example II is then imaged as follows in a xerographic mode: The plate is corona charged to a positive potential of about 300 volts, and then exposed to a watt tungsten light source at a distance of about 16 inches for about 2 seconds to form a latent electrostatic image on the surface of said plate. The latent image is then developed by cascading electroscopic marking material across the surface containing said image. The image is transferred to a sheet of paper and heat fused to make it permanent. A good quality copy of an original is obtained by this method.

EXAMPLE IV The vitreous-antimony selenium coated plate of Example I is imaged by the method set forth in Example III. A Xerox 914 Green Lamp is used in place of the tungsten light source. A good quality image is obtained.

A series of antimony-selenium alloys were prepared by the method set forth in Example II, and compared with a standard test plate of vitreous selenium such as those shown by U.S. Patent 2,970,906 to Bixby. Both the antimony-selenium plates, and the selenium plates contained a layer of about 40 to 50 microns of the respective photoconductive layers on an aluminum substrate. Both groups of plates were compared for their sensitivity factor and relative spectral response as illustrated in FIGURES 1 and 2, respectively.

In FIGURE 1 antimony-selenium plates of varying compositions and thicknesses were tested by the electrostatic contrast potential scanner in order to determine their speeds relative to selenium under given (Xerox 2400 Machine) conditions. The relative speed is illustrated by the sensitivity factor; a factor of 2 meaning that the particular alloy is 2 times faster or more sensitive than selenium. The plate is run through a cycle consisting of corona charging the plate to a constant field of twelve volts per micron (12 v./;:.), exposing the plate to reflected light measuring the potential on the plate by means of an electrometer, and then erasing all residual voltage by means of a cool white fluorescent lamp.

The plate is first exposed using light reflected from a white background with the exposure aperture varying logarithmically (3 /2) for twelve consecutive cycles. The plate is again run through the same cycles; however, this time the exposure light is reflected from a grey subject. A potential difference is then calculated between the areas discharged by the light reflected from the white and grey subjects. The point at which this potential difference is the greatest is then compared to selenium under the same conditions and this gives a relative speed with respect to the selenium standard.

The light source used in a Xerox 914 fluorescent green lamp. The residual voltage is erased by a cool white fluorescent lamp. The potential is measured by a Monroe 1264-4 dual electrometer follower, with a brush, Mark 280, dual channel strip chart recorder.

As illustrated by FIGURE 1, the addition of antimony to selenium increases the sensitivity from a factor of 2 at about 6.0 percent to a factor of 12 times that of selenium at about 14 percent antimony.

As shown in FIGURE 2 the relative response of various percentages of antimony and selenium as compared with 100 percent selenium is illustrated at four different wavelengths. The relative response is based on a factor of 1.0 for 100 percent vitreous selenium at a wavelength of 0.40 micron.

The relative response is measured by first positively charging the plates under dark room conditions to a field of 12 volts per micron by corona discharge. The potential is measured by an electrometer probe. The plates are then discharged by monochromatic radiation from a Burton lamp which is a 100 watt tungsten lamp Model 1200, using Corning filters to give the appropriate wavelength as illustrated by the graph. Monochromatic radiation of 0.40, 0.50, 0.60 and 0.70 microns was used. At each particular wavelength the initial rate of discharge (loss of voltage per unit time) for the 100 percent selenium plate was measured against various antimony-selenium alloys. The relative response is measured as the ratio of the initial discharge rate of the antimony-selenium alloy to the 100 percent vitreous selenium based on selenium at 0.40 microns. The rate of discharge is measured with an electrometer.

It can be seen from FIGURE 2 that the relative response of the antimony-selenium alloys in the preferred range (about 7 to 19 percent antimony) are superior to 100 percent selenium. As the wavelength increases, the relative response of the antimony-selenium, although decreasing, still is markedly superior to that of the 100 percent selenium which is practically insensitive to radiation beyond 0.60 micron. No measured sensitivity was detected at 0.70 micron for selenium.

It can be seen that the addition of antimony to selenium, in critical amounts, results in a photoconductor exhibiting greater sensitivity and spectral response than conventional vitreous selenium.

Although specific components and proportions have been stated in the above description of the preferred embodiment of this invention, other suitable materials and procedures such as those listed above, may be used with similar results. In addition, other materials may be added which synergize, enhance or otherwise modify the properties of these plates.

Other modifications and ramifications would appear to those skilled in the art upon reading the disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A photosensitive element having a photoconductive insulating layer, said layer comprising a vitreous alloy of antimony and selenium with the antimony comprising between about 5 to 21 percent of said layer.

2. The element of claim 1 wherein the antimony is present in an amount between about 7 to 19 percent.

3. The element of claim 1 wherein the antimony is present in an amount of about 14 percent.

4. A xerographic plate having an electrically conductive support member and a photoconductive insulating layer thereon, comprising a vitreous alloy of antimony and selenium, with the antimony comprising between about 5 to 21 percent of said layer.

5. The plate of claim 4 wherein the antimony is present in an amount between about 7 to 19 percent.

6. The plate of claim 4 wherein the antimony is present in an amount of about 14 percent.

7. A method of imaging comprising:

(a) providing a xerographic plate having an electrically conductive support member and a photoconductive insulating layer thereon, comprising a vitreous alloy of antimony and selenium, with the antimony comprising between about 5 to 21 percent of said layer;

(b) forming an electrostatic image on said plate; and

(c) developing said image to make it visible.

8. The method of claim 7 wherein the antimony is present in an amount of about 7 to 19 percent.

9. The method of claim 7 wherein the antimony is present in an amount of about 14 percent.

10. A method of imaging comprising:

(a) providing a xerographic plate having an electrically conductive support member and a photoconductive insulating layer thereon, comprising a vitreous alloy of antimony and selenium, with the antimony comprising between about 5 to 21 percent of said layer;

(b) substantially uniformly electrostatically charging said plate; and

(c) exposing said plate to a pattern of activating radiation thereby forming a latent electrostatic image; and

(d) developing said image to make it visible.

11. The method of claim 10 wherein the antimony is present in an amount between about 7 to 19 percent.

12. The method of claim 10 wherein the antimony is present in an amount of about 14 percent.

References Cited UNITED STATES PATENTS 2,297,691 10 1942 Carlson 96--1 2,910,602 10/ 1959 Lubszynski et a1 2S2-501 2,962,376 11/1960 Schaffert 252-501 NORMAN G. TORCHIN, Primary Examiner J. R. HIGHTOWER, Assistant Examiner US. Cl. X.R. 

